This invention relates generally to semiconductor devices and methods for making the same. More particularly, this invention relates to optically triggered semiconductor devices employing thyristor devices and methods for making the same.
Thyristor devices, such as silicon controlled rectifiers (SCRs) have been widely used as switching devices in a variety of applications, such as motor controls, home appliances, power converters, and light dimmers due to their fast response time, regenerative action and low resistance thereof once triggered. Typically, the thyristor devices are used as power semiconductor switches that permit large electrical currents to be switched at high voltages.
Normally, the thyristor devices are triggered to be electrically conductive by applying a trigger current to their gate terminals, while the anode and cathode terminals thereof are forward biased. Once triggered, the gate trigger current may be removed without turning off the thyristor devices. The thyristor devices become low-impedance current paths and remain in the conductive state until an electric current flowing between the anode and cathode terminals is reduced below a minimum value called the holding current. Alternatively, the anode and cathode terminals may be reverse biased to turn off the thyristor devices.
There have been various ways to trigger the thyristor devices through the gate terminals thereof. For optically triggered thyristors, an incident light is applied to a thyristor device to generate a trigger current through by means of the photoelectric effect to trigger the thyristor device. Using incident light to trigger thyristor devices for high voltage applications is advantageous because the incident light can be isolated from the anode and cathode terminals of the thyristor devices.
However, some high voltage applications require that the electric current between the anode and cathode terminals of the thyristor devices be high. As a result, an optically generated trigger current may not be large enough to trigger such thyristor devices. This can limit the use of such thyristor devices to low voltage and current applications.
Therefore, there is a need for new and improved optically triggered semiconductor devices employing the thyristor devices and methods for making the same, so that the thyristor devices can operate in high voltage and/or high current applications.